1. Field of the Invention
The invention relates to an approaching vehicle detecting system and approaching vehicle detecting method that detect an approaching vehicle on the basis of sounds collected by a plurality of sound collectors mounted on a host vehicle.
2. Description of Related Art
In an approaching vehicle detecting system, an ambient sound is collected by a plurality of sound collectors, and the moving direction of a sound source (particularly, the running sound of a vehicle) is identified on the basis of an arrival time interval between the collected sounds. In the system described in Japanese Utility Model Application Publication No. 5-92767 (JP 5-92767 U), frequency components in a low-frequency band and a high-frequency band each are removed by a band pass filter from electrical signals output from a plurality of microphones arranged at a predetermined interval to be converted to corrected electrical signals, power in a predetermined frequency band in which the feature of the running sound of a vehicle appears is calculated from the corrected electrical signals, it is determined that there is an approaching vehicle when the power level is higher than a predetermined value, and unnecessary noise components are removed from the corrected electrical signals to be converted to noise reduction signals, the cross correlation between the noise reduction signals of the plurality of microphones is computed, and the approaching direction of the approaching vehicle is computed from an arrival time interval at which the correlation is maximum.
In the above described approaching vehicle detecting system, in order to detect a vehicle that approaches in the transverse direction of a host vehicle, a plurality of microphones are arranged horizontally with respect to the host vehicle (parallel to a road surface). However, the inventors of the present application found a new challenge in process of development. That is, when a plurality of microphones are arranged horizontally in this way, not only a vehicle that is running on a road in the same plane as the host vehicle but also a vehicle that is running on a road vertically different in position from the host vehicle (for example, a road above the host vehicle (elevated road), a road below the host vehicle) is also detected as an approaching vehicle. That is, there is no difference in the arrival time interval between sounds collected by a plurality of horizontally arranged microphones between a sound source present in the same plane as the host vehicle and a sound source present above or below the host vehicle, so it is difficult to distinguish whether a sound source is in the same plane as the host vehicle. In this way, in the existing approaching vehicle detecting system, a sound source in a vertically different plane, which is unlikely to collide with the host vehicle, may also be detected as an approaching vehicle. As a result, an unnecessary alarm, or the like, about the detected approaching vehicle is issued, so the reliability of a safety system decreases.